5 Differences Between Rainbow Trout vs Steelhead Trout Explained

The exact classification of rainbow trout and steelhead trout may need to be clarified. Some consider them separate subspecies of the genus Oncorhynchus Mykiss. In contrast, others are certain that rainbow trout is the subspecies and steelheads are nothing more than a migratory form of rainbow trout.

Rainbow and steelhead trout have subtle physical differences. Both are born in freshwater, but only rainbow trout remain and live there. Steelhead trout migrate to the ocean, where they live until they return to their freshwater place of birth to spawn. 

Even if some anglers are right when they say that steelheads are ocean-based rainbow trout, the two have different features listed here.

The genus Oncorhynchus mykiss is the scientific name for the rainbow trout, while steelheads are often considered saltwater-based rainbow trout.  

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Lifestyle

Rainbow Trout are freshwater species, and steelheads are generally considered saltwater species. All Oncorhynchus Mykiss are born in a freshwater lake, river, stream, creek, or pond, but rainbow trout remain there throughout their lives, and steelheads migrate to a freshwater location.

Steelheads are anadromous, meaning they hatch in freshwater, and after a period of between 6 months and three years, they answer an urge to move downstream to saltwater. During spawning, steelheads return to their birthplace to spawn. 

Size, Weight, and Color  

Other differences between steelheads and rainbow trout relate to their physical features. Steelheads are bigger. They are up to 45 inches long and weigh between 6 and 40 lbs. Rainbow trout is about half the size of steelheads, with a maximum length of 26 inches. They also weigh less, between 2 lbs. and 9 lbs. 

Rainbow trout has a pink-to-white and reddish stripe on either side of its back, with some blue, green, and black spots on the back, fins, and tail. 

Steelheads have little left of the pink stripe they had at birth. With time their color may range from dark silver to white, green, or steely blue, a potential explanation for their name. They have small spots along their back and on their head.

Shape

Steelheads are rounder and heavier than rainbow trout, and their heads are round. Their shape helps to conserve energy and supports their bulky body as they swim in the sea’s challenging currents. Living in the ocean leaves its mark on steelheads, who may carry scars and look haggard. 

A rainbow trout’s shape is elongated or ‘torpedo-shaped.’ Their body is leaner than steelheads’. Their upper jaw is short and does not reach past the eye. Their pelvic, anal, and dorsal fins have a white edge or tip. 

Habitat

To understand rainbow trout’s habitat choice, one needs to concentrate on a significant life event for the fish – spawning. Rainbow trout live all their lives in a spawning-perfect habitat.  

For spawning to succeed, rainbow trout require rivers and streams with the correct temperature, fast water flow, and a high oxygen level. Rainbow trout prefer spawning in cold water, at 42-52 degrees Fahrenheit. Higher temperatures shorten the spawn. The stream flow is vital, as well.

A fast, constantly flowing stream of clean, highly oxygenated water at the right temperature over the nests helps steelheads spawn. Another imperative to rainbow trout spawning is the river bottom, which rainbow trout prefer to be gravel and sand because it serves as a filter, ensuring the water is clear. 

Anadromous steelhead trout spend the early part of their lives in freshwater before migrating to the ocean, a very different habitat. Depending on the climate and the condition of the water, some steelheads stay for some time in the estuary – where the ocean’s salty water mingles with the stream’s freshwater, before moving into the ocean itself, where they swim along the food-rich Pacific Ocean. 

This habitat accounts for steelheads being much bigger than rainbow trout. After a few years in the ocean, steelheads return to their birthplace and spawn in the freshwater. 

Diet

Adult steelheads move from the zooplankton of their early life to eat whatever is available in the Pacific Ocean habitat, such as insects, mollusks, smaller fish, crustaceans, and larger animals such as mice if they can manage to swallow them. 

Rainbow trout eat zooplankton and graduate to mostly water insects and larval-like water fleas. Later they add to their diet water insects, like the caddisfly, whose larvae are aquatic and adults are terrestrial.  

Protection and Conservation 

Rainbow trout are plentifully available in North American water, along the Pacific Ocean in the west and the Atlantic Ocean in the east. They are considered an invasive species as they affect native fish. Rainbow trout are strong and disease resistant, spawning in large quantities when young. 

Historically, rainbow trout were grown in hatcheries and released into streams to accommodate anglers. As a result, rainbow trout proliferated even where they were overfished and where they did not spawn well.   

On the other hand, anadromous (that is, freshwater-born fish that migrate to the ocean’s saltwater), like steelhead trout, have been badly affected by difficulties in the migratory process to and from the ocean. 

Steelheads are listed under the Endangered Species Act (ESA), which protects and conserves imperiled species. The main reasons for the decline of steelheads are a hybridization of rainbow trout with other species, dam building that blocks fish’s migratory routes, and the release of polluting materials into various streams. 

Frequently Asked Questions

Do Rainbow Trout Turn Into Steelhead?  

Rainbow trout remain rainbow trout. They continue to live and spawn in freshwater. Steelhead trout stay in fresh water and, after an initial period that ranges from 6 months to 3  years, they migrate to the ocean. Some define steelheads as saltwater rainbow or seawater trout, while others see them as different species.  

Can You Substitute Steelhead Trout For Rainbow Trout? 

Anglers will likely find steelhead trout in the ocean and saltwater estuaries. Steelheads are bigger than rainbow trout. 

To increase the number of steelheads over the number of rainbow trout, some hatcheries control steelheads’ journey from the ocean upstream, where they spawn, and separate the steelheads from the rainbow trout. With time, the ratio between rainbow trout and steelhead trout will change in favor of steelheads,

Is A Steelhead A Salmon Or A Trout?

While steelheads belong to the salmon family, they are trout, not salmon. When salmon go upstream to spawn, it dies shortly after spawning. On the other hand, steelheads go upstream, spawn, and remain at the spawning location before returning to the ocean.  

What Is The Difference Between Trout And Rainbow Trout?

Rainbow trout is a freshwater fish. It lives its life in streams and lakes. Some trout, like the steelhead trout, spend the early part of their life in freshwater, after birth, before migrating to the ocean. 

Final Thoughts

Anglers and scientists have been trying to find a clear differentiation between rainbow trout and steelhead trout. While one can see differences in coloration, size and weight, shape, diet, and levels of protection the two receive, it becomes increasingly accepted that the most evident difference between them is their lifestyle choice of a habitat: freshwater vs. the ocean.